1. Field of the Invention
The present invention relates to a multi-antenna integration module, particularly to a multi-antenna integration module having a common unit.
2. Description of the Related Art
With the popularization of wireless communication, there are also many advances in antenna technology. Particularly, many types of integrated antenna systems have been developed to meet the tendency of miniaturizing antennae and fabricating multi-frequency communication devices, wherein different antenna structures are integrated into a single antenna module to decrease the resonant length of antennae and reduce the size of antenna systems.
Refer to FIG. 1a for a conventional assembly antenna of a dual-mode device. The conventional assembly antenna comprises a ground plane 13, a first antenna 14, a second antenna 15, a first coaxial feeder cable 16 and a second coaxial feeder cable 17. The rectangular ground plane 13 has a first ground point 132 and a second ground point 133. The first antenna 14 is arranged near an upper edge 131 of the ground plane 13 to implement the operation of a first network. The second antenna 15 is also arranged near the upper edge 131 of the ground plane 13 to implement the operation of a second network. The abovementioned antenna structure can satisfy the requirement of multi-frequency communication systems, such as a dual-frequency communication device or a dual-frequency WLAN (Wireless Local Area Network) system.
Refer to FIG. 1b and FIG. 1c for the measurement results of the return loss and isolation of the first antenna and the second antenna of the prior art. When defined by a return loss of less than −7.3 dB, the operation bandwidth of the first antenna covers the frequency bands of the GSM (21), DCS (22) and PCS (22) mobile communication systems. The first antenna has an isolation of less than −20 dB. The operation bandwidth of the second antenna covers the 2.4 GHz (31) and 5 GHz (32) frequency bands of WLAN. The second antenna also has an isolation of less than −20 dB.
The first antenna 14 and the second antenna 15 of the prior art have a traditional Planner Inverted F Antenna structure. When the first antenna 14 and the second antenna 15 are integrated into a single antenna module, they have to be separated by an appropriate spacing (d) to prevent from radiation interference. Thus, the overall dimensions of the antenna structure increase. As the spacing between the two antennae is hard to control, the radiation efficiency of the integrated antennae is also hard to increase. Further, antenna isolation is also likely to be limited in the prior art.